Method and apparatus for reinforcing and consolidating earth structures

ABSTRACT

A reinforcing and or confining structure for an earth formation comprising a plurality of anchor members anchored at spaced intervals in an earth formation, the anchor members being connected to the adjacent anchor members by tensile members to form a substantially continuous tensile member adjacent the surface of the ground formation. Point loads resulting from earth movements are dissipated as a tensile load throughout the system. The anchor members may be tensionable to reinforce the earth formation. The tensile elements may be formed integrally with the anchor members in a substantially L-shaped configuration or they may be separate therefrom. The substantially continuous tensile members may be formed in spaced parallel rows or they may overlap or be interconnected to form a mesh-like structure.

This invention is concerned with a method and apparatus for reinforcingand consolidating earth structures such as mine shafts and tunnels.

Where a tunnel or drive penetrates an earth structure it is oftennecessary to reinforce or otherwise confine the wall surfaces (includingthe roof) against collapse. Reinforcement or confinement has beenachieved by steel or timber shoring members and props or fabricated archmembers, but these are expensive and unsatisfactory for modern daymining techniques, particularly given the rates of tunnelling nowpossible. These are known as "passive" support systems as they onlybecome effective once the earth formation fails and collapse occurs.

Of recent years dynamic support of tunnel surfaces (particularly theroof) has been achieved by the use of devices generally known as rockanchors or roof bolts. A plurality of bore holes are drilled to adesired depth in the roof, generally transversely of the direction ofprogress of the tunnel. The roof bolts are then inserted into the boreholes and are anchored, either by mechanical means such as wedging or bygrouting with chemical or cementitious materials, at their remote innerends. The end of the bolt adjacent the bore hole opening is screwthreaded such that with the aid of a large washer and a threaded nut,the bolt may be tensioned. Tensioning of the bolts in this mannercreates zones of compression within the earth structure surrounding thebolts. By carefully selecting the bolts spaced overlapping compressionzones can be achieved to create, in effect, a reinforced arch structure.

In earth formations where the mechanical properties of the formationwould require very close spacing of bolts, reinforcement is achieved bybolting a steel strap to the wall surface with rock bolts intermediatethe ends of the girder. These straps (which may include reinforcing ribsor channels) are generally arranged transversely of the direction ofprogress of the tunnel and, if required, may include props adjacent theends of the strap. Such straps may be of any suitable length but, ingeneral, do not exceed six meters as they become too difficult tohandle.

With the combination of compression zones and supported zones, a dynamicreinforced arch is thus created.

The use of steel straps in conjunction with roof bolts is generallyconfined to soft, crumbly or highly faulted earth formations such ascoal seams, fragmented rock etc., or areas which may be subjected tohigh induced stresses as a result of adjacent mining action.

In either of the abovementioned "dyanmic" systems, support orreinforcement against earth formation outbursts is confined to aplurality of adjacent transverse "arches". If the region surrounding oneor more of the rock bolts fails, tension in the rock bolt can reduce tozero with the result that the integrity of the reinforced "arch" failswith the likelihood of collapse. Further, if a reinforced "arch" failsor collapses, the stress release in the earth formation can causeadjacent "arches" to lose their integrity with a resultant massivecollapse.

Neither of the above systems of earth formation reinforcement permitsdissipation of outburst stresses to any substantial degree whereby theoutburst can be resisted or supported against collpase. The steel strapmay support very small portions of loosened earth formation in theimmediate vicinity of the strap but no meaningful support is availablebetween adjacent straps. Steel straps are generally constructed of lightgauge steel and obtain a degree of flexural rigidity from being rolledor otherwise formed into a corrugated cross-section, generallyconforming to a "W" in shape. These straps do not fully utilize thepotential tensile strength of such a relatively large mass of steel.Firstly, it is not known in mining practice to interconnect these straps(apart from patterns of say two lengths at tunnel intersections) to forman elongate tensile member of "substantially continuous" length(hereinafter defined). Thus in use, the ability of the strap to supportan earth mass is dependent entirely on the anchoring member and theflexural strength imparted by the cross-sectional deformation. Secondly,even if such straps were to be connected in "substantially continuous"lengths, the effective tensile strength then becomes a function of theresistance to tearing in the region where the anchor passes through thestrap. Accordingly, only a relatively small portion of the cross sectionof the strap is utilized when a rock-bolted strap is subjected to atensile load parallel to an earth face against which it is mounted.

In the event of an outburst there is no increase in stress on the rockbolts of a simple compression "arch" rather the tension in the bolts isreleased. Where a strap is employed with rock bolts, an outburst mayincrease the tension in the bolts and apply a flexural load to the strapitself but, the only dissipation of stresses which can occur is withinthe discrete strap/arch structure and not to the surrounding regions.

A further disadvantage relating to known reinforcement systems is thatin the event of an outburst there is substantially no inherent abilityto confine and restrain loosened material from falling.

It is known to use either a welded wire mesh or a chain wire mesh inconjunction with tensionable rock bolts in an endeavour to confine earthmasses which might otherwise fall from between those regions"reinforced" by the rock bolts. Because of the difficulties in overheadhandling of relatively large panels of mesh in relatively confinedspaces it is customary to use small panels. Accordingly the tensileelements comprised in the mesh panels are effectively discontinuous overany substantial area. This lack of tensile continuity will, underoutburst conditions, enable considerable convergence of the earth masswith the result that there is a general loss of integrity in thestressed area which can ultimately lead to loss of anchorage in the rockbolt as convergence continues.

It is an aim of the present invention to overcome or alleviate thedisadvantages of prior art earth formation reinforcement systems and toprovide a reinforcement system with inherent confinement ability.

According to one aspect of the invention there is provided a method ofreinforcement of earth formations against convergence comprising thesteps of:-anchoring a plurality of anchor members in an earth formation;and connecting tensile elements between adjacent anchor members to forma substantially continuous tensile member adjacent the surface of theearth formation, whereby in use a force generated by said earthformation is distributed as a tensile stress in said substantiallycontinuous tensile member.

Preferably said anchor members comprise tensionable anchor members.

Preferably said anchor members comprise rock bolts anchorable in a borehole by mechanical means.

Preferably said anchor members comprise rock bolts anchorable in a borehole by grouting composition.

Preferably the normally free ends of said anchor members are adapted forsubstantially rigid connection to said tensile elements.

Preferably said tensile elements are integrally formed with said anchormembers.

Preferably said tensile elements are connected to said anchor members toform a linear substantially continuous tensile member.

Preferably said tensile elements are connected to said anchor members toform one or more multi-directional substantially continuous tensilemembers.

Preferably said tensile elements are connected to said anchor members toform a net-like multi-directional substantially continuous tensilestructure.

Preferably a plurality of tensile elements are connected to a pluralityof said anchor members to form a net-like multi-directionalsubstantially continuous tensile structure.

According to another aspect of the invention there is provided areinforcing and/or confining structure for an earth formation comprisinga plurality of anchor members anchored at spaced intervals in said earthformation, at least some of said anchor members being connected toadjacent anchor members by tensile elements to form a substantiallycontinuous tensile member adjacent the surface of said ground formation.

Preferably, a plurality of said tensile elements are connected to anchormembers to form a net-like substantially continuous tensile structure.

According to yet a further aspect of the invention there is provided ananchor member comprising an insertable portion for anchoring in an earthstructure and a normally free portion adapted for connection to atensile element.

Preferably said tensile element is formed integrally with said anchormember.

Preferably said anchor member is tensionable within a bore hole.

According to yet a further aspect of the invention there is provided atensile element for connection between anchor members comprising a bodyportion and means for connection to at least one anchor member.

Preferred embodiments of the invention will now be described withreference to the accompanying drawings in which:

FIG. 1 is a cross sectional view showing schematically installation of atensile member in an earth formation.

FIGS. 2-6 show a number of alternative arrangements.

FIG. 7 shows one embodiment of an anchor member according to theinvention.

FIGS. 8-15 show alternative embodiments of tensile elements according tothe invention.

FIG. 16 shows a combination anchor/tensile element.

FIGS. 17-18 show the use of tensile members in accordance with theinvention in conjunction with conventional rock bolts.

FIG. 19 illustrates the layout for a test procedure.

FIG. 20-27 are graphical representations of test results obtained fromthe arrangement of FIG. 19.

FIG. 28 is a plan view of the linkage between adjacent members of analternative form of a tensile element according to the invention.

FIG. 29 is a front elevational view of the arrangement of FIG. 28.

FIG. 30 is a side elevational view of a link means between a tensileelement and an anchor member.

FIG. 31 is a plan view of the arrangement shown in FIG. 30.

In FIG. 1, anchor members 1 such as rock bolts are anchored in boreholes 2 in an earth formation 3 such as the roof or walls of a mineshaft, tunnel or the like.

Between adjacent anchor members 1 are rigidly connected tensile elements4 adjacent the surface 5 of the earth formation. The generally rigidtensile elements 4 are connected to the anchor members 1 in such amanner as to form a substantially continuous tensile member 6 extendingover the surface 5 of the earth formation.

In the event of a rock outburst, strain release within the earthformation generates or is accompanied by a convergent force, generallyshown by arrow A in a direction outwardly from the earth surface. As thetensile member 6 is situated substantially against or adjacent thesurface 5, the convergent force is distributed almost immediately as atensile force into the tensile member 6 shown by the double arrows.

It will be noted that, with the possible exception of immediatelyadjacent anchor members, the only force applied to the anchor members isa shear force. Generally speaking there is substantially no tensileforce applied to the anchor members which might otherwise pull theanchor members out of their bore hole or at least weaken the retentionof the anchors.

It will be noted also that as the convergent or outburst force isdissipated directly into the tensile member 6, the determinant factorfor withstanding outburst forces is the tensile strength of the tensilemember.

Thus not only does such a structure reinforce an earth formation but italso serves to confine weakened earth masses against collapse. It isbelieved that the dissipation of the outburst force as a tensile stressin the tensile member enables the reinforcing and confining propertiesof the present invention to be largely independent of the nature of theearth formation. This contrasts markedly with all known earth formationreinforcing systems which are substantially discontinuous in nature.

The anchor members which may be employed with the present invention maycomprise any of the presently used rock bolts. Rock bolts are generallydivided into two main categories--mechanically anchored, i.e. wedges, orgrout retained, i.e. by chemical or cementitious grouts. These rockbolts are tensionable by a threaded nut on the free end of the bolt tocreate a compression zone in the earth formation. The threaded nut onthe free end enables ready mechanical connection of a tensile elementbetween adjacent rock bolts to form a generally rigid substantiallycontinuous tensile member. As described later the tensile elements maybe associated with the bolts directly or with a washer or plate clampedbetween the nut and the earth surface. The anchor member may alsocomprise a mechanical wedge, the subject of co-pending Australian PatentApplication No. PG 1404, the contents of which are incorporated hereinby reference.

Although in some circumstances it may be desirable to reinforce theearth formation by tensioning at least some of the rock bolts, the mainfunction of the bolts (anchoring means) is to retain the resultanttensile member closely adjacent the surface of the earth formation.Accordingly immense cost savings could be achieved by reducing both thelength and gauge of the bolts. In addition, less sophisticated (and thusless expensive) mechanical retaining means or grouting systems are alsopossible.

Generally linear tensile members as shown in FIG. 1 could be arrangedlongitudinally of a tunnel or shaft either singly or in spaced rowsdepending on the nature of the earth formation. Alternatively the lineartensile members could be arranged helically within the tunnel extending,from one wall, over the roof to the opposite wall. For additionalreinforcement and confinement, the linear tensile members may beinterconnected or even crossed.

Alternative configurations exemplary of an almost unlimited variety ofpatterns are shown generally in FIGS. 2-6.

In FIG. 2 the arrangement comprises a plurality of linear tensilemembers interconnected at alternating anchor members.

In FIG. 3 a mesh-like structure is formed by interconnecting alladjacent anchor members.

The arrangement of FIG. 4 comprises a mesh-like structure in whichlinear tensile members are overlaid or interwoven but not connected atthe intersections.

FIGS. 5 and 6 show mesh-like structures comprised respectively of threeand four axes of linear tensile members. These structures may beoverlaid, interwoven and/or interconnected at some or all of theintersections of linear tensile members.

FIG. 7 illustrates an alternative embodiment of the invention. A rockbolt 7 is anchored into a bore hole by any convenient means. Over theprotruding threaded stem of the bolt is placed a length of channel 8with webs facing outwardly from the surface of the earth formation. Thechannel includes an aperture through which the stem of the bolt passes.A tensile element 10 comprising a wire rope, cable or steel rod is thenclamped into the channel recess by a second inverted channel section 9which locates within the recess of channel 8. The rock bolt is thentensioned by a nut and washer assembly 12. Tensioning of the rock boltrigidly clamps tensile element 10 into a locked relationship with thebolt. By interconnecting the tensile element to adjacent tensionablerock bolts there is obtained a substantially continuous tensile elementextending over the surface of the earth formation. If required,additional tensile strength may be obtained by using a second tensileelement 11 extending parallel to first tensile element 10. Alternativelythe arrangement may be employed as a means for connecting theterminations of separate tensile elements or it may be employed topermit interconnection between adjacent arrays of tensile elements.

For interconnections of linear tensile members or for formation ofmulti-directional or mesh-like structures, a number of connectingtensile elements are shown in FIGS. 8-14.

In FIG. 8 the tensile element comprises simply a continuous elongateloop 13 of rod or bar steel formed by welding the ends. The loop may beof any suitable length but generally will represent the spacing ofadjacent anchor members or twice that spacing. In the embodiment shownthe loop is placed over the free ends of adjacent rock bolts 14, 15 toform a tensile element therebetween. A rigid connection between bolts 14and 15 is achieved by adding a washer and nut (not shown) to the freeends of the bolts and either tightening the nut or tensioning it.Interconnections between other rock bolts are achieved in a desiredmanner by connecting further loops 13a in the manner described above.

In the case where the length of the loop represents twice the normalrock bolt spacing, the loop may bridge an intermediate bolt shown inphantom at 16. This intermediate bolt may also form the pont ofintersection of two or more of such loops.

FIG. 9 illustrates a modification of the device of 8 in which a plate orwasher 17 is attached intermediate the ends of the loops. If required aloop may be attached on either side of washer 17 to form a cruciformmember.

FIG. 10 illustrates a tensile link element with an adjustable centreconnection. The centre connection comprises a plate or washer 18 with abolt aperture 19 and a slit 20. The edges of the slit are displacedrelative to each other to permit loop 21 or other tensile element to beslidably located therein. In this manner the position of the centre boltmay be varied as required. It is considered important to restrain thelimbs of the loop against sideway movement under load as otherwise theycould be forced out from under the intermediate plate 18 and thus losesupport.

FIG. 11 shows a tensile element shaped from rod on bar steel.

FIG. 12 shows an element with integrally formed eyes at either end.

FIGS. 13 and 14 show multi directional variations of the elements ofFIGS. 10 and 12 respectively.

FIG. 15 illustrates a most preferred embodiment comprising flat barsteel punched at appropriate intervals to accommodate varying anchorspacings. The punched steel strip may be supplied conveniently in fixedlengths as flat strip or could be provided in coil form.

FIG. 16 illustrates a combined anchor member/tensile element 22 formedfrom a length of steel rod. The member 22 is formed by shaping the rodinto a U-shaped member and then bending the U-shaped member at a desiredposition intermediate its length to form an inverted L-shaped member.Member 22 thus comprises an anchor portion 23 and a tensile elementportion 24. Anchor portion 23 can be mechanically retained in a borehole by forming links 25 or the like. If a more positive anchoring isrequired anchor portion 23 (or at least the free end thereof) can beretained in a bore hole by a grout. An anchored tensile member can beformed by locating subsequent bore holes for successive units inside andadjacent the end of loop 26 at the outer free end of each U-shapedmember 22. In this manner a substantially continuous tensile member maybe formed.

FIG. 17 shows an alternative reinforcing and confining structurecomprising an array of substantially continuous tensile members inconjunction with conventional rock bolts. Tensile elements 28 such asthose illustrated in FIG. 16 are suitably formed as spaced, anchoredsubstantially continuous tensile members 29 and are arrangedlongitudinally of the walls of a tunnel or the like. Rock bolts 30 arearranged in any suitable pattern in the spaces between members 29 tocombine the advantages of both types of structure. Preferably, the rockbolts are arranged so as to create, when tensioned, a plurality ofspaced compression arches transversely of the tunnel.

FIG. 18 illustrates yet a further configuration comprising an anchorednet-like tensile structure 31 in combination with conventional roofbolts 32.

It will be readily apparent to a skilled addressee that many differingpatterns, configurations and combinations of anchoring devices andtensile elements can be arranged to suit the particular requirements ofan earth formation.

FIG. 19 illustrates a simple test which can be carried out todemonstrate the effectiveness of the invention and to compare thevarious embodiments thereof.

Portions of 6 mm diameter steel rod were arranged on a flat concretesurface in the configuration shown. Dimension y represented a distanceof 2·0 meters consistent with the depth of insertion of a rock bolt in abore hole. Dimension x was 1·2 meters and is typical of anchor spacing.

Intersections 33 were each welded to form the analogue of asubstantially continuous tensile member 34 attached to anchor members35. The free ends 36 of the anchor members 35 are welded to steel plates37, which in turn are secured to the concrete surface by masonry anchors38. This is analogous to securing rock bolts in a bore hole.

Steel pins 39 of approximately 25 mm diameter were embedded into theconcrete surface with portion of the pin protruding upwardly to locatethe intersections 33. This was intended to be analogous to the locationof an intersection at the entrance to a bore hole. The end 40 ofsubstantially continuous tensile member 34 was welded to a steel plate41 in turn secured to the concrete surface by a masonry anchor 42.

An hydraulic ram 43 was firmly secured to the concrete surface bymasonry anchors and a steel plate 44 was placed between piston 45 andtensile member 34 to act as a load spreading member.

Strain gauges were then attached to "tensile elements" 1,3,5,7, and 9and the "anchor members" 2,4, and 6.

Hydraulic ram 43 was then actuated to create a set of conditionsanalogous to a strain release in the surface of an earth formation suchas a tunnel, shaft or the like. The strain values detected by straingauges 46 were recorded and presented graphically as shown in FIGS.20-27.

FIGS. 20 and 21 illustrate strain decay in the tensile elements as afunction of distance from the force applied. It can be seen clearly thatstrain decays rapidly in the tensile member over a relatively shortdistance even for a wide range of applied forces.

FIG. 22 and 23 illustrate similar characteristics for the anchormembers.

The rapid decay of strain vs distance from load applied indicated thatan outburst force (which is substantially perpendicular to the surfaceof an earth formation or at least has a substantial perpendicularvector) is restrained by a resultant tensile reaction in the tensilestructure parallel to the surface of the earth formation. The rapiddecay of tensile forces is considered to occur as a result ofcompressive forces applied in the earth formation adjacent the surfacethereof.

In the event of a burstout there is thus considered to be an activereinforcement as well as an active and passive support to the earthformation. As the resultant of the outwardly directed (convergent)burstout force is a lateral compressive force, reinforcement of theearth formation occurs.

Both the reinforceing and confinement properties of the invention areconsidered to arise from the substantially non-yielding and rapidlyreacting nature of the substantially continuous tensile structure.

As used throughout this specification, the term "substantiallycontinuous" refers to the interconnection of tensile elements to formsubstantially rigid tensile members or structures over distances of saymore than 15 meters of an earth formation surface "substantiallycontinuous" tensile members are distinguished in the present inventionfrom steel or timber reinforcing beams or "W" straps which have beenhitherto used in lengths up to 6 meters but have not been interconnectedto form a "substantially continuous structure".

FIGS. 24 and 25 show values of strain in the individual tensile elementsas a function of load applied. Expectedly, those tensile elementsclosest the force applied show a substantially directly proportionalrate of increase of strain. The rate of increase of strain decaysrapidly as the distance increases from the point of applied load. Thesubstantially constant strain value in element 9 suggests that thetensile structure may be capable of withstanding immense loadsregardless of load applied. Accordingly, the main determinant in loadbearing capabilities of such a structure would be the tensile strengthof the tensile elements.

FIGS. 25 and 26 show similar values of strain in the anchor membersversus applied load.

The test results illustrated in FIGS. 20-27 clearly demonstrate theefficacy of the present invention to reinforce and confine earthformations.

FIG. 28 illustrates yet another form of tensile element according to theinvention. The element comprises a generally L-shaped length of steelrod which may have a smooth or deformed surface. One limb of theL-shaped member comprises an anchor member (not shown) for insertioninto a bore hole for anchoring by grouting or mechanical means. Theother limb 49 of the L-shaped member comprises a tensile member adaptedto lie adjacent an earth surface. The free end 50 of the limb comprisingthe tensile member has a first bend 51 in the same plane as the earthsurface against which it lies and a second bend 52 in a direction normalto the plane of the earth surface and away therefrom.

To install this type of tensile element a bore hole is formed and theanchor limb of the L-shaped element is suitably anchored in the borehole. In the region of the crook of first bend 51 a second bore hole isdrilled. A base plate 53 comprising a base 54 with a central aperture 55and raised walls 56 is then located between the end of the tensileelement and the earth surface with the aperture 55 aligned with the borehole.

The anchoring limb of a second tensile element 57 is then insertedthrough aperture 55 into the bore hole for anchoring therein.

As shown in FIG. 29 the bend 58, between the insertable limb and thetensile limb of element 57, fits snugly into the respective crooks ofbends 51 and 52. A further plate 59 having an aperture for the free end50 of limb 49 is placed over the aperture and the entire arrangement istensioned by means of threaded nut 60. It will be seen that tensioningof nut 60 will cause tension to be induced into anchoring limb 61 oftensile element 57 as well as the tensile limbs of both tensile elements49 and 57. Substantially continuous anchored tensile members may thus beconstructed over the surface of an earth formation with both theanchoring portion and the tensile portion in a state of tension.

The arrangement described above is considered to be particularlysuitable for softer or fractured earth formations such as coal seamswherein initial reinforcement of the formation may be induced in amanner similar to conventional rock bolt or rock bolt/steel straptechnology. This arrangement offers the additional advantage that if theanchoring reinforcement fails then dynamic confinement reinforceing ofthe earth formation takes over.

If required, a further aperture 62 may be included in plate 59 to enableinjection of a grout material to rigidify the intersection of adjacenttensile elements.

The tensile elements illustrated in FIGS. 28 and 29 may be arranged instaright linear arrays or, possibly, in a zig-zag formation due to theability of the intersection between adjacent tensile elements enablingrelative rotation through about 120°.

FIG. 30 shows an alternative embodiment of the arrangement illustratedin FIG. 7.

A compression member 63 comprises an apertured U-shaped plate with abase 64 which engages against an earth surface 65. The outer leg 66(shown in phantom in its initial position) is spaced from base 64 at adistance to neatly accommodate a tensile member 67. Member 63 isapertured to receive the free end of a rock bolt 68 therethrough. Aclamp member 69 comprises an angle section member having a slottedaperture 70 to receive the free end of rock bolt 68 to enable clampmember 69 to slide between an extended position (as shown in phantom)whereby a further tensile member 71 (also shown in phantom) may beclamped, and a retracted position as shown.

When a single tensile member is to be clamped the downwardly extendinglip 72 of clamp member 69 engages the upper surface of outer leg 66 andas tension is applied to rock bolt 68 by nut 73, leg 66 is deformed toclamp tensile member 67 under compression.

FIG. 31 shows a plan view of the arrangement of FIG. 30.

What is claimed is:
 1. A method of supporting and confining an earthformation wherein a plurality of anchor members are anchored into spacedboreholes in an exposed surface of the earth formation, each anchormember having connected thereto a tensile element lying against thesurface of the earth formation and extending away from such anchormember towards an adjacent borehole, which method comprises connecting afree end of each tensile element to a captive portion of an adjacenttensile element connected to an anchor member anchored in such adjacentborehole, each tensile element being connected to the respective tensileelement to form a substantially continuous tensile member extendinglinearly over the surface of the earth formation whereby in use suchsubstantially continuous tensile member operates to distribute a loadapplied by the earth formation as a tensile stress in such substantiallycontinuous tensile member along the connected tensile elements, andwherein a plurality of the anchor members and thereto connected tensileelements each is formed by a respective elongate U-shaped steel memberbent intermediate its ends to form an L-shaped member having a first armin the form of a closed loop and a second arm in the form of two freeends, the first arm forming the tensile element and the second armforming the anchor member.
 2. A method as claimed in claim 1, whereinthe anchor members having tensile elements connected thereto arearranged in spaced boreholes in the earth formation to form a pluralityof substantially continuous tensile members extending linearly over thesurface of the earth formation.
 3. A method as claimed in claim 2,wherein the substantially continous tensile members are arranged toextend parallel to each other across the surface of the earth formation.4. A method as claimed in claim 3, wherein the parallel substantiallycontinuous tensile members are interconnected at intervals to form amesh-like array of substantially continuous tensile membersinterconnected by tensile elements extending transversely therebetween.5. A method as claimed in claim 2, wherein the substantially continuoustensile members are arranged to extend across the surface of the earthformation in an angular relationship to form a mesh-like array with somesubstantially continuous tensile members overlying others.
 6. A systemfor supporting and confining an earth formation comprising a pluralityof anchor members anchored into spaced boreholes in an exposed surfaceof the earth formation, each anchor member having connected thereto atensile element lying against the surface of the earth formation andextending away from the anchor member towards an adjacent borehole, afree end of each said tensile element being connected to a captiveportion of a tensile element connected to an anchor member anchored insaid adjacent borehole, each said tensile element being connected to arespective adjacent tensile element to form a substantially continuoustensile member extending linearly over the surface of the earthformation whereby in use said substantially continuous tensile memberoperates to dissipate a load applied by the earth formation as a tensilestress in said substantially continuous tensile member along saidconnected tensile elements, and wherein a plurality of said anchormembers and thereto connected tensile elements each are formed by arespective elongate U-shaped steel member bent intermediate its ends toform an L-shaped member having a first arm in the form of a closed loopand a second arm in the form of two free ends, said first arm includingthe tensile element and said second arm including the anchor member. 7.A system as claimed in claim 6, wherein said anchor members havingtensile elements connected thereto are arranged in spaced boreholes inthe earth formation to form a plurality of substantially continuoustensile members extending linearly over the surface of the earthformation.
 8. A system as claimed in claim 7, wherein said substantiallycontinuous tensile members are arranged to extend parallel to each otheracross the surface of the earth formation.
 9. A system as claimed inclaim 8, wherein said parallel substantially continuous tensile membersare interconnected at intervals to form a mesh-like array ofsubstantially continuous tensile members interconnected by tensileelements extending transversely therebetween.
 10. A system as claimed inclaim 7, wherein said substantially continuous tensile members arearranged to extend across the surface of the earth formation in anangular relationship to form a mesh-like array with some substantiallycontinuous tensile members overlying others.
 11. A system for supportingand confining an earth formation comprising a plurality of restrainingelements each having an L-shape providing an anchor portion and atensile portion, at least one and another restraining element each beingformed by an elongate rod-like steel member bent upon itself to providea loop at the free end of the tensile portion and generally parallelsections coextending from said loop to form said tensile portion andthen generally at right angles to said tensile portion to form saidanchor portion, said one restraining element having its anchor portionanchored in a respective borehole in the earth formation with itstensile portion extending over the surfacce of the earth formationtoward an adjacent borehole in which the anchor portion of said anotherrestraining element is anchored, and said another restraining element atthe captive end of its tensile portion passing through the loop at thefree end of the tensile portion of said one restraining element therebyto connect the tensile portion of said one restraining element to thetensile portion of said another restraining element.
 12. A system as setforth in claim 11, wherein respective pluralities of said restrainingelements each have the tensile elements thereof connected to adjacenttensile elements thereof to form respective substantially continuoustensile members extending linearly over the surface of the earthformation, and said substantially continuous tensile members arearranged to extend generally parallel to each other across the surfaceof the earth formation.
 13. A system as set forth in claim 12, whereinsaid generally parallel substantially continuous tensile members areinterconnected at intervals by other said restraining elements extendingtransversely therebetween to form a mesh-like array of substantiallycontinuous tensile members.
 14. A system as set forth in claim 11,wherein respective pluralities of said restraining elements each has thetensile elements thereof connected to adjacent tensile elements thereofto form respective substantially continuous tensile members extendinglinearly over the surface of the earth formation, and said substantiallycontinuous members are arranged to extend across the surface of theearth formation in an angular relationship to form a mesh-like arraywith some substantially continuous tensile members overlying others. 15.A system for supporting and confining an earth formation comprising aplurality of restraining elements each having an anchor portion and atensile portion extending generally at right angles to each other, saidrestraining elements being formed from elongate rod-like steel membersand said tensile portion being bent at its free end first in a directionperpendicular to the anchor portion and then in a direction parallel tothe anchor portion to form a hook, at least one said restraining elementhaving its anchor portion anchored in a respective borehole in the earthformation with its tensile portion extending over the surface of theearth formation towards an adjacent borehole in which the anchor portionof another said restraining element is anchored, and said anotherrestraining element at the captive end of its tensile portion havinginterlocked therewith the hook at the free end of the tensile portion ofsaid one restraining element thereby to connect the tensile portion ofsaid one restraining element to the tensile portion of said anotherrestraining element.
 16. A system as set forth in claim 15, whereinrespective pluralities of said restraining elements each have thetensile elements thereof connected to adjacent tensile elements thereofto form respective substantially continuous tensile members extendinglinearly over the surface of the earth formation, and said substantiallycontinuous tensile members are arranged to extend generally parallel toeach other across the surface of the earth formation.
 17. A system asset forth in claim 16, wherein said generally parallel substantiallycontinuous tensile members are interconnected at intervals by other saidrestraining elements extending transversely therebetween to form amesh-like array of substantially continuous tensile members.
 18. Asystem as set forth in claim 15, wherein respective pluralities of saidrestraining elements each has the tensile elements thereof connected toadjacent tensile elements thereof to form respective substantiallycontinuous tensile members extending linearly over the surface of theearth formation, and said substantially continuous members are arrangedto extend across the surface of the earth formation in an angularrelationship to form a mesh-like array with some substantiallycontinuous tensile members overlying others.
 19. A system for supportingand confining an earth formation comprising a plurality of tensileelements each being formed by an elongate steel member bent to form aloop at each end, said tensile elements extending across the surface ofthe earth formation with loops at the ends of said tensile elementsoverlapping loops at the ends of other tensile elements at respectiveboreholes in the surface of the earth formation, and rock bolts anchoredin said boreholes, said rock bolts having stems extending through saidrespective overlapped loops of said tensile elements to interconnectsaid tensile elements.
 20. A system as set forth in claim 19, whereinrespective pluralities of said tensile elements each have adjacenttensile elements thereof connected by said rock bolts to form respectivesubstantially continuous tensile members extending linearly over thesurface of the earth formation, and said substantially continuoustensile members are arranged to extend generally parallel to each otheracross the surface of the earth formation.
 21. A system as set forth inclaim 20, wherein said generally parallel substantially continuoustensile members are interconnected at intervals by other said tensileelements extending transversely therebetween to form a mesh-like arrayof substantially continuous tensile members.
 22. A system as set forthin claim 19, wherein respective pluralities of said tensile elementseach have adjacent tensile elements thereof connected by said rock boltsto form respective substantially continuous tensile members extendinglinearly over the surface of the earth formation, and said substantiallycontinuous tensile members are arranged to extend across the surface ofthe earth formation in an angular relationship to form a mesh-like arraywith some substantially continuous tensile members overlying others.